This invention relates to a copper alloy lead material for leads in semiconductor devices, and more particularly to such a copper alloy lead material which possesses excellent strength, heat resistance, soldering reliability, etc.
A conventional method of manufacturing a semiconductor device such as an integrated circuit (hereinafter called "IC") and a large scale integration (hereinafter called "LSI") comprises, for instance, the following main processes (a)-(g):
(a) preparing a metal strip, e.g. a copper alloy strip for leads having a thickness within a range from 0.1 to 0.3 mm as a material for leads of the semiconductor device; PA0 (b) stamping the strip for leads into a lead frame having a shape suitable for use in the semiconductor device which is to be manufactured; PA0 (c) mounting semiconductor chips in which are incorporated elements such as semiconductor elements of high purity Si, Ga - As alloy, or the like, on the lead frame at its predetermined surface portions, either by hot bonding using a conductive resin such as Ag paste, or by thermocompression bonding through one or more plating layers of at least one metal selected from the group, consisting, e.g. of Au, Ag, and Ni which has been previously plated on the surface of the strip or the lead frame; PA0 (d) connecting elements of the semiconductor chips to the lead frame by wire bonding using Au wires or the like; PA0 (e) encapsulating the semiconductor chips, the wire bonding portions, the surface portions of the lead frame on which the semiconductor chips have been mounted, etc. by a plastic resin or the like for protection of same; PA0 (f) cutting the lead frame along boundaries between adjacent ones of the semiconductor chip-mounted surface portions, to form leads of the semiconductor device; and PA0 (g) plating the whole or part of the surfaces of the leads with a solder of an Sn - Pb alloy or the like by dipping or electroplating, so as to enable soldering of the leads to the substrate of the semiconductor device. PA0 (1) Excellent stampability, as well as formability (for bending and coining); PA0 (2) High heat resistance enough to be free of thermal strain as well as thermal softening when semiconductor chips are bonded to a lead frame stamped from the material for leads; PA0 (3) Excellent heat radiation, i.e. electrical conductivity (since the heat radiation, i.e. the thermal conductivity is proportional to the electrical conductivity, the heat radiation can be measured in terms of electrical conductivity); and PA0 (4) High strength enough to be free of breakage during transportation of the semiconductor device or when the leads are repeatedly bent in connecting them to wiring boards during mounting of the semiconductor device into an electrical device or an electronic device. PA0 Iron: from 1.5 to 3.5% by weight; PA0 Phosphorus: from 0.01 to 0.15% by weight; PA0 Zinc: from 0.03 to 0.2% by weight; and PA0 Copper and inevitable impurities: the balance, PA0 Tensile Strength (for evaluation of the strength): of the order of 49-50 Kgf/mm.sup.2 ; PA0 Elongation (for evaluation of the stampability, as well as formability for bending and coining): of the order of 4%; PA0 Electrical Conductivity (for evaluation of the heat radiation and electrical conductivity): of the order of 60-70% I.A.C.S. (International Annealed Copper Standard); and PA0 Softening Point (for evaluation of the heat resistance): of the order of 350.degree.-360 .degree. C. PA0 Iron: from 2 to 2.4 percent by weight; PA0 Phosphorus: from 0.001 to 0.1 percent by weight; PA0 Zinc: from 0.01 to 1 percent by weight; PA0 Magnesium: from 0.001 to 0.1 percent by weight; and PA0 Copper and inevitable impurities: the balance. PA0 (a) melting the copper alloy into a molten copper alloy having a predetermined chemical composition; PA0 (b) preparing a material for leads from the molten copper alloy; PA0 (c) forming the material for leads into a lead frame having a shape suitable for use in the semiconductor device which is to be manufactured; PA0 (d) mounting semiconductor chips on the lead frame at its predetermined surface portions; PA0 (e) connecting elements of the semiconductor chips to the lead frame by wire bonding; PA0 (f) encapsulating at least the semiconductor chips, wire bonding portions, and surface portions of the lead frame on which the semiconductor chips have been mounted; PA0 (g) cutting the lead frame along boundaries between adjacent ones of the semiconductor chip-mounted surface portions, to form leads of the semiconductor device; and PA0 (h) plating at least part of surfaces of the leads by a solder, so as to enable soldering of the leads to the substrate of the semiconductor device. The copper alloy consists essentially of from 2 to 2.4 percent by weight iron, from 0.001 to 0.1 percent by weight phosphorus, from 0.01 to 1 percent by weight zinc, from 0.001 to 0.1 percent by weight magnesium, and the balance of copper and inevitable impurities.
A copper alloy material for leads of a semiconductor device is required to satisfy the following properties:
A conventional typical copper (Cu) alloy material for leads comprising a Cu alloy consisting essentially of:
which satisfies the required properties, has been proposed, e.g. by Japanese Patent Publication No. 45-10623 (corresponding to U.S. Pat. No. 3,522,039), and has been widely used as a material for leads of semiconductor devices.
The conventional Cu alloy material for leads possesses the following satisfactory properties:
However, in recent years, it has been required for materials for leads to possess further improved strength and heat resistance for use as leads, with increased wiring densities in semiconductor devices.
Further, although the above-mentioned conventional Cu alloy material for leads possesses satisfactory adhesion to the solder used in soldering the leads to the substrate of the semiconductor device, it has low soldering reliability such that when it is used as leads of the semiconductor device, the soldered portions of the leads often exfoliate or peel off from the substrate in use of the semiconductor device, which can cause malfunction of the device.